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LakeQuality
C

Long Lake

Polk County, WisconsinEutrophic

Long Lake sits at a C on the grading scale — not impaired, not pristine, with summer measurements that vary year to year. Clarity is the limiting factor — phosphorus is reasonable but suspended particles or algal cells keep water transparency below Wisconsin norms.

At a TSI of 51, Long Lake reads as eutrophic — nutrient-rich enough that summer algal growth and reduced clarity are expected, not unusual. A maximum depth of 17 ft puts Long Lake in the middle of Wisconsin's depth distribution. At 273 acres, Long Lake fits the Wisconsin median for monitored lakes, with partial shoreline records. Long Lake ranks 62 of 77 in Polk County — at the lower end of the locally monitored distribution.

An invasive species record — Banded Mystery Snail — has been logged at Long Lake; Wisconsin DNR maintains the official infested-waters list. Bass fishing is part of the appeal: the species list runs to 3, anchored by largemouth and/or smallmouth bass. Public access is available — the lake is on the Wisconsin DNR public-access list. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.

Source: EPA Water Quality Portal sampling records, Wisconsin DNR Surface Water, last sampled 2025-09-23. Grade methodology: LakeGrade methodology.

Swimming Safety

Generally safe for swimming, moderate water quality

Water Quality Grade: C, Fair

Murky, only visible to about 5.9 ft. Phosphorus level: 26.1 µg/L. Trophic State Index: 51.

MetricValueGrade
Water Clarity (Secchi Depth)5.9 ftD
Phosphorus26.1 µg/LB
Chlorophyll-a (Algae)No data
Trophic State Index (TSI)51Eutrophic

High nutrients, frequent algae, reduced clarity

Lake Details

CharacteristicValue
Maximum Depth17 ft
Surface Area273 acres
Public AccessYes

Fish Species

Click a species to see all Wisconsin and Minnesota lakes where it is found.

→ Best fishing times for Long Lake (14-day solunar calendar)

→ Is it safe to eat fish from Long Lake? (mercury & PFAS guide)

Long Lake fishing regulations (limits, seasons, special rules)

Invasive Species

Banded Mystery SnailChinese Mystery SnailCurly-Leaf Pondweed

Water Quality Trend: Improving

Based on 7 years of monitoring data (2020-2025).

MetricTrendChange/YearYears
Water Clarity Improving+0.604 m/yr7
Phosphorus Improving-1.54 µg/L/yr6
See year-by-year chart →

Recreation & Access

2
Boat Landings
Yes
Public Access

Location

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County Ranking

Ranked #62 of 77 lakes in Polk County

Cleaner Lakes Within 30 Miles

Long Lake holds Grade C. 5 nearby lakes hold higher grades.

See full comparison →

Nearby Lakes in Polk County

Eutrophic Lakes in Wisconsin

WI DNR Lake Profile

Authoritative data from the Wisconsin DNR LakePages. Monitored by volunteers since 1992. 2 stations on file (most recent sample 2025).

DNR Assessment
Good · Shallow Seepage lake
Trophic State Index 53 (eutrophic) · 5-year average

Fish Species (DNR-rated)

Panfish(Common)Largemouth Bass(Common)Northern Pike(Common)

Data Sources

Water quality data from the EPA Water Quality Portal

Grading methodology based on Metropolitan Council standards

Fish and recreation data from Wisconsin DNR Lakes

Most recent sample: 2025-09-23

Monitoring stations: 1